As a result of changes in the composition of refuse or garbage over the last few years, and particularly due to the increase in caloric value of such material, the combustion grate is exposed to high thermal stresses, particularly certain individual portions thereof. Due to the dual function of the combustion grate as a combustion support with ventilating means and also as a transfer or conveyance means for the material to be burned, the grate structure often includes such features as alternating fixed and movable grate sections and is a relatively complex multi-part structure. In addition, because such a combustion grate is part of a control loop and is expected to have an appropriately rapid response to a control signal, its dynamics must have a certain minimum degree of precision. Thus, boundary conditions must be insured in which the combustion grate can operate in a reliable manner, partly by special interventions to prevent the equilibrium which commonly occurs.
One of a large number of important boundary conditions is the grate temperature. The specific control intervention involves establishing combustion temperature control such that the average temperature of the grate layer does not exceed 300.degree. C. with a combustion temperature of, for example, 1000.degree. C.
It is well recognized that local overheating of the grate layer due to heat accumulation leads to increased corrosion and an increased scale formation rate and, finally, to the complete destruction of parts of the grate layer within a relatively short time. These grate layer parts must be replaced and, thus, interchangeability is desired and is achieved by various structural arrangements.
One preventative measure for preventing high corrosion or scaling rates and increased mechanical wear which leads to the premature destruction of larger units is provided by the forced cooling of the grate layer. Almost without exception, part of the cooling air is additionally used as the primary combustion air in the prior art. Thus, the control of the primary combustion air is also a temperature control measure.
For forced cooling purposes, the undergrate blast generally flows against the grate layer and air passage openings in the layer allow part of the cooling medium to pass into the refuse bed to be burned where it participates in the combustion process as the primary combustion air. Clogging of the air openings leads to reduced flow and increased back pressure in the cooling air path and, consequently, to accumulation of heat at the particular point of the grate layer. This leads to thermal overstressing of the grate part, increased wear, higher scaling rates and, within a short time, to the destruction of the grate part.